Lecture8 - IS2150/TEL2810 JamesJoshi AssociateProfessor,SIS...

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1 IS 2150 / TEL 2810 Introduction to Security James Joshi Associate Professor, SIS Lecture 8 Nov 2, 2011 Key Management Network Security
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2 Objectives Understand/explain the issues related to, and  utilize the techniques  Key management  Authentication and distribution of keys Session key, Key exchange protocols Mechanisms to bind an identity to a key Generation, maintenance and revoking of keys Security at different levels of OSI model Privacy Enhanced email IPSec
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3 Notation X     Y  : {  Z  ||  W  }  k X , Y X  sends  Y  the message produced by  concatenating  Z  and  W  enciphered by key  k X , Y which is shared by users  X  and  Y A     T  : {  Z  }  k A  || {  W  }  k A , T A  sends  T  a message consisting of the  concatenation of  Z  enciphered using  k A A ’s key,  and  W  enciphered using  k A , T , the key shared by  A  and  T r 1 r 2  nonces (nonrepeating random numbers)
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4 Interchange vs Session Keys Interchange Key Tied to the principal of communication Session key Tied to communication itself Example Alice generates a random cryptographic key  k s   and uses it to encipher  m She enciphers  k s  with Bob’s public key  k B Alice sends {  m  }  k s   k s   k B Which one is session/interchange key?
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5 Benefits using session key In terms of Traffic-analysis by an attacker? Replay attack possible? Prevents some  forward search attack Example: Alice will send Bob message that is  either “BUY” or “SELL”.  Eve computes possible ciphertexts {“BUY”}  k B   and  {“SELL”}  k B Eve intercepts enciphered message, compares,  and gets plaintext at once
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6 Key Exchange Algorithms Goal:  Alice, Bob to establish a shared key Criteria Key cannot be sent in clear Alice, Bob may trust a third party All cryptosystems, protocols assumed to be  publicly known
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7 Classical Key Exchange How do Alice, Bob begin?  Alice can’t send it to Bob in the clear! Assume trusted third party, Cathy Alice and Cathy share secret key  k A Bob and Cathy share secret key  k B Use this to exchange shared key  k s
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8 Simple Key Exchange  Protocol Alice Cathy { request for session key to Bob } k A Alice Cathy { k s } k A , { k s } k B Alice Bob { k s } k B Alice Bob { m } k s What can an attacker, Eve, do to subvert it?
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This note was uploaded on 12/01/2011 for the course INFSCI 2501 taught by Professor Jjoshi during the Spring '11 term at Pittsburgh.

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Lecture8 - IS2150/TEL2810 JamesJoshi AssociateProfessor,SIS...

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